Carrier billing lets you buy apps, games, or services by charging the cost...

https://extra-wiki.win/index.php/What_Should_I_Look_for_on_My_Bill_to_Spot_Carrier_Billing%3F

Carrier billing lets you buy apps, games, or services by charging the cost directly to your phone bill. If you have a monthly plan, the purchase is added to your next bill. If you use pay-as-you-go credit, the amount is deducted from your balance